This invention relates generally to humidity sensing and more specifically to sensing humidity in a computer tape backup library.
Since the advent of programmable information processing systems, the need to store information has grown dramatically. Information storage is frequently accomplished through devices, which interconnect with a computer and act relatively independently of it in response to signals received from the main data processing functions of the computer. These devices, known as peripheral devices, act to receive data from the main computer memory and then to store such data on a separate media within the peripheral device. One of the aspects of typical memory devices and computer systems is their volatility. They may unintentionally lose their contents occasionally. This may be due to hard disk failures, computer virus attacks, or other reasons. To overcome these limitations, backup devices have evolved. Such devices serve the simple function of separately storing large amounts of data on relatively non-volatile media. In the field of these specialized devices, the use of magnetic tape media has become one of the most used. After data is stored on magnetic tapes, the tapes may be stored in a controlled environment that reduces the probability of the data on the tapes being corrupted. One of the parameters that may be controlled in order to reduce tape failures is humidity.
Humidity may affect, how well or if at all, a magnetic tape functions. Tape failures due to humidity may cause downtime and loss of data. It is important therefore, to track the occurrence of downtime and data loss as a function of relative humidity (%RH). When a correlation between the occurrence of downtime and data loss versus %RH is established, a %RH value may be chosen which results in the lowest occurrence of downtime and data loss. In addition, %RH measurements may be used to indicate when the %RH in the area where the tapes are stored is deviating from an ideal value. In this way, tape failures may be reduced by correcting the %RH to a proper level before failures occur. In order to most effectively track failures based on %RH, measurement of %RH should be as accurate as possible.
The invention measures the relative humidity of an environment and stores the data for later reference or immediate display. The invention uses a capacitor whose capacitance is a function of the relative humidity sensed by the capacitor. This capacitor is used in conjunction with a comparator to output a series of pulses. The frequency of these pulses is dependent on the capacitance of the capacitor and is counted by a counter that sends data to a microprocessor where the count is mapped to a relative humidity value. This value can then be stored for reference or displayed immediately.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing, illustrating by way of example the principles of the invention.